The present invention relates to a system and a method for manufacturing thin plate by hot working, and more particularly to a system for manufacturing a plate by hot working and a method for manufacturing a plate by hot working suitable for stably manufacturing high quality plates using a compact manufacturing system.
In a conventional system for manufacturing thin plate by hot working, a slab having a thickness of more than 200 mm is casted using a continuous casting machine. The slab, as a base material, is single-directionally or reversely rolled to produce a bar material using a plurality of coarse rolling mills. Then the bar material is rolled to a given thickness using a plurality of tandem finishing rolling mills for finishing and is subsequently wound up using a down coiler coiling unit to form a steel strip. The system for manufacturing thin plate by hot working described above is used in massive production plants and requires an extremely huge system having a length from a heating furnace in the up-stream end to a wind-up machine in the downstream end which is more than 300 m (meters).
In recent years, it has been regarded as important to recycle iron scrap due to generation of a massive amount of iron scrap. Thus there is a desire in the industry to distributively install small scale and small production manufacturing plants rather than to concentrate production at a large scale and massive production manufacturing plant. Consequently there arises a need for a small scale rolling mill system.
For obtaining a small scale system, there have been various methods and systems proposed to decrease the number of rolling mill stands. For example, in Japanese Patent Application Laid-Open No. 63-90303 (1988), there is proposed a hot working rolling mill system where at least one among a set of hot working rolling mills is a reverse rolling mill, and an edger is provided in the inlet side or in the outlet side of the reverse rolling mill.
Another method for obtaining a small scale system is to decrease the number of rolling mill units by increasing the plate thickness reduction amount per rolling operation. For example, in Japanese Patent Application Laid-Open No. 63-132703 (1988), there is proposed a method where rolling is performed by at maximum three or four roll stands of rolling mills provided in the process following a continuous casting machine. In this system two of the roll stands in the front stage have large diameter working rollers.
Another method proposed for obtaining a small scale system is to decrease the number of roll stands of rolling mills or the number of passing-through times for rolling by improving efficiency of rolling. For example, in Japanese Patent Application Laid-Open No. 55-22500 (1980), there is proposed a method where a coarse rolling mill working under a high pressure is arranged in the front of a line of finishing rolling mills.
The system described in Japanese Patent Application Laid-Open No. 63-90303 (1988) has a disadvantage in that a complex handling technique is required in performing reverse rolling and, in addition to this, a wide space is required for treating plates after passing-though times for rolling of even numbers in the front side of a finishing rolling mill since reverse coarse rolling is performed using one or more pairs composed of a reverse rolling mill and an edger which are installed in the set of rolling mills and then finishing tandem rolling is performed using the whole of the rolling mills.
The system described in Japanese Patent Application Laid-Open No. 63-132703 (1988) has a disadvantage in that the system becomes large-scale and complex since the large diameter working rollers increase the load of rolling and larger diameter reinforcing rollers having sufficient shaft strength for carrying the rolling loads are required.
Further, the system described in Japanese Patent Application Laid-Open No. 55-22500 (1980) has a disadvantage in that a slab pushing apparatus and a slab drawing apparatus are required to perform the coarse rolling under the high pressure rolling condition. Thus the rolling method and rolling system are complex, and a space for the slab drawing apparatus is required between the coarse rolling mills operating under the high pressure rolling condition and the finishing rolling mills.
The present invention is made under the situation described above. An object of the present invention is to provide a system and method for manufacturing a plate by hot working which is capable of stably manufacturing high quality plates using a compact manufacturing system having a short overall system length.
The present invention makes it possible to provide a system and method for manufacturing a plate by hot working which is capable of stably manufacturing high quality plates using a compact manufacturing system by combining and installing sets of rolling mill stands having small diameter working rollers and a splicing machine for thin plates to assure continuous engaging capability of the rolling mill stands having the small diameter working rollers.
According to one aspect of the invention, the above noted object is achieved according to the present invention by providing a system for manufacturing thin plate by hot working having a set of finish rolling mill stands for hot rolling thin plate from its case thickness to a finish thickness, the rolling mill stands having indirectly driven small diameter working rollers, and a splicing machine for continuously splicing said thin plate located upstream of these rolling mill stands. In preferred embodiments of the invention the thin plate is cast to a thickness of less than 100 mm and the working rollers of the finish rolling mill stands have a diameter substantially smaller than conventional working rollers of 700 mm-800 mm. In preferred embodiments of the invention the diameter of the working rollers is less than 600 mm and working roller diameters between 300 mm and 400 mm are especially preferred.
In this description, the terms "non-driven" and "indirectly driven" are used to describe working rollers which are not rotatably driven by driving means engaged at the working roller end portion (or neck portions) outside the location of the strip being rolled. These "non-driven" and "indirectly driven" working rollers are instead driven by supporting rollers in the form of backup rollers for four-high mill stands and intermediate rollers for six-high mill stands.
According to another aspect of the present invention, a front edge press for tapering the front edge portion of said thin plate and a splicing machine for continuously splicing said thin plate are provided in the process precedent to the set of rolling mills with small diameter non-driven or indirectly driven working rolls.
According to another aspect of the present invention, in a system for manufacturing thin plate by hot working having a set of rolling mills for rolling thin plate, a rolling mill having non-driven or indirectly driven small diameter working rollers is arranged downstream of a splicing machine for continuously splicing said thin plate, a winding-off coiler is provided upstream of the splicing machine, a tunnel furnace for taking up, transferring and discharging a coil of plate is provided upstream of the winding-off coiler, a winding-up coiler is provided upstream of the tunnel furnace, a soaking pit is provided upstream of the winding-up coiler, one or more continuous casting machines for casting thin plate are provided upstream of the soaking pit, and a down-coiler or a chain wrapper is provided downstream of the set of rolling mills.
According to another aspect of the present invention, in a system for manufacturing thin plate by hot working having a set of rolling mills for rolling thin plate, a rolling mill having non-driven or indirectly driven small diameter working rollers is arranged downstream of a splicing machine for continuously splicing said thin plate, a heating furnace capable of discharging said thin plate is provided upstream of the splicing machine, a soaking pit capable of taking-up, transferring and discharging said thin plate is provided upstream of the heating furnace, one or more continuous casting machines for casting thin plate are provided upstream of the soaking pit, and a down-coiler or a chain wrapper is provided in the process downstream of the set of rolling mills. This system is a low cost compact system requiring minimal space and length of the production line.
In certain preferred embodiments of the invention, a front edge press for tapering the front edge portion of said thin plate has anvil blocks with a taper portion and a parallel portion. With this arrangement, unnecessary moving of the thin plate is eliminated and smooth pressing can be performed. This tapered front edge portion facilitates start up engagement or "biting" of a strip of plates with the working rollers.
In certain preferred embodiments of the invention, a front edge press for tapering the front edge portion of said thin plate includes rotatable upper and lower anvil blocks, an off-set being provided between a line connecting between the upper and the lower rotating centers of the anvil blocks and the minimum bite gap portion between the upper and the lower anvil blocks. With this arrangement, unnecessary contact between the thin plate and the anvil blocks is eliminated and smooth pressing can be performed. This tapered front edge portion facilitates start up engagement or "biting" of a strip of plates with the working rollers.
In certain preferred embodiments a machine is provided for increasing the friction coefficient between the working rollers at a first mill stand and a plate to be rolled.
In certain preferred embodiments, the machine for increasing friction coefficient is a machine to grind a working roller installed in a rolling mill, for example, a rotating grinding stone.
In certain preferred embodiments, the machine for increasing friction coefficient is a machine for forming projections and depressions on the surface of the front edge of a thin plate.
In certain preferred embodiments, the machine for increasing friction coefficient is a machine for supplying friction increaser between a roller and a plate to be rolled.
In certain preferred embodiments the splicing machine comprises a cutter for cutting the rear edge of a precedent plate and the front edge of the following plate, a melt-planing device having a plurality of melt-planing torches arranged in the width direction of the plate, transferring means for moving said melt-planning torches in the width direction of the plate, and pressing means for applying pressing force to the interface of the rear edge of the precedent plate and the front edge of the following plate.
In certain preferred embodiments of the invention, the splicing machine comprises cutting means for cutting the rear edge of a precedent plate and the front edge of the following plate, induction heating coils arranged at the upper and the lower surfaces of said plate to inductively heat the butt surfaces of the plates, and pressing means for applying pressing force to the interface of said butt surfaces.
In certain preferred embodiments of the invention, the splicing machine comprises cutting means for cutting the rear edge of a precedent plate and the front edge of the following plate, arc generating means for locally generating arc by conducting current in the gap between butt surfaces of the plates, arc transferring means for moving said arc generating means in the width direction of the plate, and pressing means for applying pressing force to the butt interface of the rear edge of the precedent plate and the front edge of the following plate.
In certain preferred embodiments of the invention, the splicing machine comprises cutting means for cutting the rear edge of a precedent plate and the front edge of the following plate, oxygen gas jetting means for jetting oxygen gas to at least one edge surface of the rear edge of the precedent plate and the front edge of the following plate, iron powder mixing means for mixing iron powder in the oxygen gas, and pressing means for applying pressing force to the contacting surfaces of the rear edge of the precedent plate and the front edge of the following plate.
In certain preferred embodiments of the invention, the splicing machine comprises cutting means for cutting the rear edge of a precedent plate and the front edge of the following plate, plate vibrating means for vibrating at least one of the rear edge of the precedent plate and the front edge of the following plate, and pressing means for applying pressing force to the contacting surfaces of the rear edge of the precedent plate and the front edge of the following plate.
In certain preferred embodiments of the invention, the splicing machine comprises pressing means for superposing and pressing the rear edge of the precedent plate and the front edge of the following plate, sliding means for sliding the rear edge of said precedent plate and the front edge of said following plate superposed and pressed against each other, and means for forming at least one indent portion on at least one of the superposed surfaces of the rear edge of said precedent plate and the front edge of said following plate.
In certain preferred embodiments of the invention, the splicing machine comprises thinning means for thinning each of the rear edge of the precedent plate and the front edge of the following plate, pressing means for superposing and pressing the rear edge of the precedent plate and the front edge of the following plate thinned with said thinning means, sliding means for sliding the rear edge of said precedent plate and the front edge of said following plate superposed and pressed against each other, and said thinning means having means for forming at least one indent portion on at least one of the superposed surfaces of the rear edge of said precedent plate and the front edge of said following plate.
Each of these above-noted arrangements for performing the continuous splicing of plates provides for economical and efficient splicing which facilitates the achievement of the overall desired minimum size compact system.
In certain preferred embodiments of the invention, the set of rolling mills or stands are constructed such that at least a first front rolling mill stand or first and second front rolling mill stands are four-high rolling mill stands. Thus, these first or first and second stage rolling mill stands are advantageously of a small compact size.
In certain preferred embodiments of the invention, the set of rolling mill stands are constructed such that at least a first front rolling mill stand or first and second front rolling mill stands have working rollers made of a material for high temperature and the other downstream rolling mill stands have working rollers made of a material for low temperature, the materials for the working rollers being different from each other. With this arrangement, it is possible to roll a comparatively high temperature plate and maintain relatively high temperature rolling operations.
In certain preferred embodiments of the invention, at least one rolling mill stand among said set of rolling mill stands is a rolling mill stand wherein the working rollers are adjustably movable in the direction of the working roller axes. This arrangement facilitates maintenance of high quality rolled plate.
In certain preferred embodiments of the invention, at least one rolling mill stand among said set of rolling mill stands is such a rolling mill stand that the upper and the lower working rollers are adjustably crossed in the horizontal plane with respect to each other to vary the gap between the rollers. This arrangement further facilitates maintenance of high quality rolled plates.
In certain preferred embodiments of the invention, at least one rolling mill stand among said set of rolling mill stands is a six-high rolling mill stand that has intermediate rollers capable of moving in the axial direction and a working roller bender. This arrangement further facilitates maintenance of high quality rolled plates.
According to an aspect of the present invention, in a method for manufacturing steel strip by hot working using a system for manufacturing thin plate by hot working having a set of rolling mill stands for rolling thin plate, the method comprises continuously splicing a precedent thin plate and the following thin plate, then rolling said thin plates using said set of rolling mill stands, including at least one mill stand having non-driven or indirectly driven small diameter working rollers, to manufacture a steel strip,
According to another aspect of the present invention, in a method for manufacturing steel strip by hot working using a system for manufacturing thin plate by hot working having a set of rolling mill stands for rolling thin plate, the method comprises tapering the front edge of a thin plate using a front edge press, then rolling the thin plate using the set of rolling mill stands having non-driven or indirectly driven small diameter working rollers when said thin plate is rolled in the first place by said set of rolling mill stands and continuously splicing a precedent thin plate and the following thin plate, then said thin plates are rolled by said set of rolling mill stands using said set of rolling mill stands having non-driven or indirectly driven small diameter working rollers to manufacture a steel strip from the thin plates following the first thin plate. The tapering by the front edge press facilitates the start up of rolling by accommodating entry of the leading edge into the working rollers.
According to another aspect of the present invention, in a method for manufacturing thin plate by hot-working having a set of rolling mills for rolling thin plate, the method comprises, in rolling a first plate using said set of rolling mills, rolling a plate to be rolled using the set of rolling mills with a rolling mill having non-driving small diameter working rollers after engaging said plate in a state of increasing friction coefficient between the roller and said plate, and in rolling the plates following the first plate using said set of rolling mills, rolling the plate to be rolled using said set of rolling mills having non-driving small diameter working roller after continuously splicing the rear edge of a precedent plate to the front edge of the following plate.
According to another aspect of the present invention, in a method for manufacturing steel strip by hot working using a system for manufacturing thin plate by hot working having a set of rolling mill stands for rolling thin plate, the method comprises casting a thin plate using one or more continuous casting machines, winding up the thin plate to form a coil-shape using a winding-up coiler, warming or heating said coil-shaped thin plate in a tunnel furnace, winding off the coil-shaped thin plate warmed or heated in said tunnel furnace, continuously splicing said thin plate wound-off, rolling said thin plates which are spliced by said set of rolling mill stands having non-driven or indirectly driven small diameter working rollers, and winding up said rolled thin plate using a down-coiler or a chain wrapper.
According to another aspect of the present invention, in a method for manufacturing steel strip by hot working using a system for manufacturing thin plate by hot working having a set of rolling mill stands for rolling thin plate, the method comprises casting a thin plate using one or more continuous casting machines, warming or heating said thin plate in a soaking pit, transferring said thin plate warmed or heated in the soaking pit to a heating furnace to heat the thin plate at a given temperature in said heating furnace, continuously splicing said thin plate heated at the given temperature in said heating furnace, rolling said thin plates which are spliced by said set of rolling mill stands having non-driven or indirectly driven small diameter working rollers, and winding up said thin plate rolled using a down-coiler or a chain wrapper.
In certain preferred embodiments of the invention, the method comprises tapering the front edge portion of said thin plate using a front edge press having anvil blocks with a taper portion and a parallel portion.
In certain preferred embodiments of the invention, the method comprises tapering the front edge portion of said thin plate using a front edge press having rotatable upper and lower anvil blocks, an off-set being provided between the line connecting between the upper and the lower rotating centers and the minimum bite gap portion between the upper and the lower anvil blocks.
In certain preferred embodiments of the invention, the method of splicing said thin plates comprises cutting the rear edge of a precedent plate and the front edge of the following plate perpendicular to the rolling direction, melt-planing at least one of the rear edge of the precedent plate and the front edge of the following plate in the width direction of the rolled plate by blowing jet flow of melt-planing torches to a portion with a given width from the edge, forming a splicing surface on the edge surface by melt-planning, and applying pressing force to the splicing surfaces to splice the thin plates.
In certain preferred embodiments of the invention, the method of splicing said thin plates comprises cutting the rear edge of a precedent thin plate and the front edge of the following thin plate, butting the rear edge of the precedent thin plate and the front edge of the following thin plate with a gap between the rear edge of the precedent thin plate and the front edge of the following thin plate, inductively heating the butt surfaces of the thin plates by induction heating coils arranged at the upper and the lower surfaces of said thin plate, and applying pressing force to the interface of said butt surfaces to splice the rear edge of the precedent thin plate and the front edge of the following thin plate.
In certain preferred embodiments of the invention, the method of splicing said thin plates comprises cutting the rear edge of a precedent thin plate and the front edge of the following thin plate, butting the rear edge of the precedent thin plate and the front edge of the following thin plate with a gap between the rear edge of the precedent thin plate and the front edge of the following thin plate, conducting direct current in the gap to locally generate arc and concurrently applying an alternating magnetic field in the thickness direction of said gap to create magnetic force in the width direction to said arc, heat-melting each of the rear edge of the precedent thin plate and the front edge of the following thin plate in the width direction of the thin plates by the arc moving in the width direction of the thin plates, forming a splicing surface in each of the edges, and applying pressing force to the interface of said butt surfaces to splice the rear edge of the precedent thin plate and the front edge of the following thin plate.
In certain preferred embodiments of the invention, the method of splicing said thin plates comprises cutting the rear edge of a precedent thin plate and the front edge of the following thin plate, jetting oxygen gas and iron powder, as required, to at least one edge surface of the rear edge of the precedent plate and the front edge of the following plate to heat-melt and concurrently to blow off oxidized scales, forming a splicing surface in each of the rear edge of the precedent thin plate and the front edge of the following thin plate, and applying pressing force to the splicing surfaces to splice the rear edge of the precedent plate and the front edge of the following plate.
In certain preferred embodiments of the invention, the method of splicing said thin plates comprises cutting the rear edge of a precedent thin plate and the front edge of the following thin plate, vibrating at least one edge surface of the rear edge of the precedent plate and the front edge of the following plate to form splicing surfaces, and applying pressing force to the splicing surfaces to splice the rear edge of the precedent plate and the front edge of the following plate.
In certain preferred embodiments of the present invention, the method for splicing plates comprises the steps of superposing the rear edge of a precedent plate and the front edge of the following plate, forming at least one indent portion on at least one of said superposed surfaces, superposing and pressing the rear edge of said precedent plate and the front edge of said following plate, then sliding the rear edge of said precedent plate and the front edge of said following plate superposed and pressed against each other to join the precedent plate to said following plate.
In certain preferred embodiments of the present invention, the method for splicing plates comprises the steps of thinning each of the rear edges of a precedent plate and the front edge of the following plate, and further during thinning the edges, forming at least one indent portion on at least one of the surfaces of the rear edge of said precedent plate and the front edge of said following plate to be superposed, superposing and pressing the rear edge of said precedent plate and the front edge of said following plate, then sliding the rear edge of said precedent plate and the front edge of said following plate superposed and pressed against each other to join said precedent plate to said following plate.
In certain preferred embodiments of the invention, the method comprises rolling said thin plate using said set of rolling mill stands constructed such that at least a first front rolling mill stand or first and second front rolling mill stands are four-high rolling mills.
In certain preferred embodiments of the invention, the method comprises rolling said thin plate using said set of rolling mill stands constructed such that at least a first front rolling mill stand or first and second front rolling mill stands have working rollers made of a material for high temperature and the other downstream rolling mill stands have working rollers made of a material for low temperature, the materials for the working rollers being different from each other.
In certain preferred embodiments of the invention, the method comprises rolling said thin plate using said set of rolling mill stands constructed such that at least one rolling mill stand among said set of rolling mill stands has working rollers which are adjustably movable in the direction of the roller axis.
In certain preferred embodiments of the invention, the method comprises rolling said thin plate using said set of rolling mill stands constructed such that at least one rolling mill stand among said set of rolling mill stands has upper and the lower working rollers which are adjustably crossed in the horizontal plane with respect to each other to vary the gap between the rollers.
In certain preferred embodiments of the invention, the method comprises rolling said thin plate using said set of rolling mill stands constructed such that at least one rolling mill stand among said set of rolling mill stands is a six-high rolling mill stand that has intermediate rollers capable of moving in the axial direction and a working roller bender.
In certain preferred embodiments of the invention, the method comprises passing a dummy strip through said set of rolling mill stands in advance of rolling a thin plate in the first place, splicing said dummy strip and said thin plate, and rolling said thin plate. With this arrangement the startup rolling operating can be facilitated by controlling the size and shape off the dummy plate, such as by tapering its front end.
In certain preferred embodiments of the invention, the method comprises passing a thin plate through said set of rolling mill stands under a light pressure rolling condition when the thin plate is rolled in the first place, then rolling the thin plate under a given pressure. This arrangement also facilitates start up rolling operation by facilitating pass through at the front portion of the spliced plates to be rolled.
In certain preferred embodiments of the invention, the method comprises performing rolling by a rolling schedule in which a thick plate is rolled in the first place. This arrangement also facilitates start up of rolling of spliced together plates and also minimizes the amount of waste plate material to be thrown away.
The following has been revealed from the results of study by the inventors of the present invention.
In order to modify a conventional large scale manufacturing type to a small scale one, it is necessary to improve a hot-rolling process which is a main part of the manufacturing process. It is inevitable to improve the rolling efficiency per rolling mill or rolling mill stand, and in addition to this to make the rolling mill small in scale and size.
On the other hand, in order to improve the rolling efficiency per rolling mill stand, it is required to increase the thickness reducing amount of plate per rolling mill stand. However, in connection with increase of the thickness reducing amount of plate, there is a relationship between the limit in the thickness reducing amount of plate for engaging the front end portion of a plate and the diameter of the working rollers. Therefore, when the thickness reducing amount of plate is forced to increase beyond the limit for engaging the front edge of a plate between the working rollers, rolling of a plate cannot be performed since the plate cannot be entered between the working rollers and the working rollers slip.
In the past as a technology to cope with the problem of start rolling described above, it has been attempted to increase the limit in the thickness reducing amount of plate and accommodate engaging of the front edge of a plate between the working rollers by increasing the diameter of the working rollers. Although it is possible to increase the limit in the thickness reducing amount of a plate for engaging the front edge of a plate by increasing the diameter of the working rollers, an increase in the diameter of the working roller increases rolling load and consequently the rolling mill becomes large in size.
Reducing the number of rolling mills or mill stands with improved rolling efficiency per rolling mill stand results in large-sized rolling mills. Making rolling mill stands small in size by decreasing the diameter of the working rollers results in a great number of rolling mill stands, which contradicts the object of attaining a small scale manufacturing plant.
In the past as a technology to cope with the above, as described above, the number of rolling mill stands has been decreased by multi-passing-through rolling where rolling is performed by repeating rolling within the limit in reducing amount of plate using rolling mills capable of reversely rolling.
In another case, a pushing apparatus and a pulling apparatus have been provided and rolling under high pressure has been performed by applying force to a slab to forcibly insert the slab between upper and lower working rollers using the pushing and pulling apparatus.
As described above, although a lot of efforts have been made to increase the limit in reducing amount of plate for engaging the front edge of a plate, the front edge portion and the rear edge portion of plate, which directly relate to the limit for engaging, have been cut out and thrown away as a non-steady state rolled portion, and only a middle portion of the plate has been usable as a plate product.
Further, the length of plate in rolling by hot working is short compared to that in rolling by cold working. Consequently improving the yield of products is difficult since the ratio occupied by the front and rear portions of the plate is comparatively large, and the rolling is not efficient.
To cope with the above noted problems, a continuous rolling by hot working is described in, for example, Japanese Patent Application Laid-Open No. 4-288207 (1992). In the continuous rolling by hot working, rolled base materials are continuously spliced together in advance of a rolling process and then rolled. In this technology, it is assumed that a conventional type rolling by hot working is performed using large scale rolling mills. It is not considered to improve the efficiency of rolling itself, and a large scale rolling system for manufacturing plate is required. Therefore, the technology is not suitable for a small scale rolling system for manufacturing plate.
Incidentally, in a case where rolling is performed once a plate is engaged in rollers, it is possible to further increase the thickness reducing amount of a plate. That is, in rolling after engaging a plate, there is no geometrical condition to limit the reducing amount of plate, and rolling can be performed as far as a condition of the neutral point within the roll-bite is employed. A substantial increase in the thickness reducing amount of a plate can be realized by utilizing this characteristic and by employing a base to roll after engaging a plate in rollers. In other words, it is possible to increase the thickness reducing amount of a plate by continuously splicing rolled base materials in advance of a rolling process, rolling the spliced rolled base materials, in which most part of the plates is rolled under a steady state condition, that is, under an after-engaged condition.
Further, it is recognized by the inventors that rolling by use of small diameter working rollers can be mechanically performed by rolling under an after-engaged condition. However, the rolling load and the rolling torque in rolling by hot working are large comparing to those in rolling by cold working. Therefore, in the past, it has been considered difficult to employ small scale rolling mills and small working rollers in rolling by hot-working. This problem is approached and solved by the present invention. Since the rolling load and the rolling torque are decreased when small diameter rollers are employed, problems of mechanical strength occur in a working roller neck portion with a directly driven working roller. Since the diameter of the neck portion should be structurally made smaller as the diameter of the working roller decreases, there is a resultant difficulty in directly driving the smaller working rollers.
Furthermore, it has been avoided in rolling by hot-working to employ indirect driving of working rollers where a reinforcing roller or intermediate roller is driven, since the rolling load and the rolling torque are large and slipping occurs between the rollers. However, in fact, since the rolling load and the rolling torque are decreased by decreasing the diameter of the working roller, the inventors recognize that this does not become any problem. Therefore, it is possible to realize a rolling mill for hot-working having small diameter rollers driven by supporting rollers in the form of a backup rollers or intermediate rollers.
Since rolling is performed with small diameter rollers, a small-sized rolling mill can be used.
Further, since rolling efficiency is improved, the number of rolling mill stands can be decreased and a small scale plant can be achieved.
Furthermore, since there is no need to forcibly insert a plate between an upper and a lower working rollers using a pushing apparatus and a pulling apparatus, complex rolling is not required.
According to the present invention, most portions of a rolled material can be rolled under an after-engaged rolling condition by use of a set of rolling mill stands having non-driven or indirectly driven small diameter working rollers by continuously splicing thin plates using a splicing machine, and small scale rolling mills can be used. Thereby, it can be attained to minimize the size of a system for manufacturing thin plate.
According to the present invention, the front edge portion of a thin plate is tapered using a front edge press to engage it between rollers when the thin plate is rolled in the first place, then the thin plate is rolled using a set of rolling mills having non-driven or indirectly driven small diameter working rollers. Thereby, it becomes easy to pass the first rolled thin plate through a rolling mill, and the thrown-away part of the non-steady rolled portion can be decreased. The thin plates following the first rolled thin plate are continuously spliced using a splicing machine and the thin plate can be rolled under an after-engaged rolling condition using a set of rolling mills having non-driven or indirectly driven small diameter working rollers, and thus small-sized rolling mills can be utilized. Thereby, it can be attained to minimize the size of a system for manufacturing thin plate.
According to preferred embodiments of the invention, in order to increase the limit in thickness reducing amount of plate for engaging the front edge of a plate, there are methods where the diameter of the working roller is increased and the thickness of plate is relatively decreased. In addition to these, a method to increase the friction coefficient between a roller and a plate to be rolled is also effective. When the friction coefficient is large, the force to draw a plate into the roller bite becomes large and consequently a large reducing amount of plate can be obtained.
According to the present invention, in rolling a plate to be rolled in the first place, rolling is performed using a set of rolling mills have non-driven small diameter working rollers by increasing the friction coefficient between the roller and the plate to make the engagement possible. Thereby, it becomes easy to pass the first rolled thin plate through a rolling mill, and thrown-away parts of non-steady rolled portions can be decreased. The thin plates following the first rolled thin plate are continuously spliced using a splicing machine to roll the thin plate under an after-engaged rolling condition using a set of rolling mills having non-driven small diameter rollers, and small-sized rolling mills can be utilized. Thereby, it can be attained to make the size of a system for manufacturing thin plate small.
The machine for increasing friction coefficient according to one embodiment is a machine to grind a working roller installed in a rolling mill, for example, a rotating grinding stone. Thereby, the friction coefficient between a roller and a plate to be rolled can be increased by increasing the surface roughness of the front edge of the plate.
The machine for increasing friction coefficient according to another embodiment is a machine for supplying friction increaser between a roller and a plate to be rolled. Thereby, the friction coefficient between a roller and a plate to be rolled can be increased by supplying small solid particles into the gap between the roller and the plate.
The splicing machine according to other preferred embodiments forms at least one indent portion on at least one of the surfaces of the rear edge of a precedent plate and the front edge of the following plate in superposing said plates, superposing and pressing the rear edge of said precedent plate and the front edge of said following plate, then sliding the rear edge of said precedent plate and the front edge of said following plate superposed and pressed against each other to join said precedent plate to said following plate. The method of superposing and sliding the plates has a function to strengthen the joint strength and improve reliability since sliding length can be lengthened. The method of forming at least one indent portion on at least one of the surfaces has a function to gather the oxide scale peeled off from the superposed surface by sliding and to promote joining. Thereby, splicing the rear edge of the precedent plate and the front edge of the following plate can be easily performed, and it can be attained to minimize the size of a system for manufacturing thin plate.
According to certain preferred embodiments, the method for splicing plates comprises the steps of thinning each of the rear edge of a precedent plate and the front edge of the following plate, and further during thinning the edges, forming at least one indent portion on at least one of the surfaces of the rear edge of said precedent plate and the front edge of said following plate to be superposed, superposing and pressing the rear edge of said precedent plate and the front edge of said following plate, then sliding the rear edge of said precedent plate and the front edge of said following plate superposed and pressed against each other to joint said precedent plate to said following plate. The method of thinning the thickness of the rear edge of the preceding plate and the front edge of the following plate has a function to prevent the spliced plate thickness after being spliced from increasing. Other functions are the same as described above.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.